Attitude control strategy for unmanned wheel-legged hybrid vehicles considering the contact of the wheels and ground

During patrol and surveillance tasks, attitude control is crucial for improving the terrain adaptability of unmanned wheel-legged hybrid vehicles. This paper proposes an attitude control strategy for unmanned wheel-legged hybrid vehicles, considering the contact of the wheels and ground. The proposed method can naturally achieve torque control efficiently of each joint actuator and wheel-side actuator and avoid the discrepancy between off-road terrain and stability. First, an inverse kinematics model is established to resolve the body and each joint rotation angle, and the dynamic model is built based on the multi rigid body theory, considering the contact points planning of wheel and ground. Considering the nonholonomic constraint of the structure scheme, a hierarchical real-time attitude controller for a wheel-legged vehicle is proposed. The upper layer calculates the contact points of each wheel and the ground through the quadratic programming algorithm, and the lower layer is divided into a legged motion generator and a wheel motion generator by a mathematical analysis method. Finally, the proposed method is applied to achieve the tracking and control of the whole-body trajectory. The proposed strategy can achieve the decoupling of wheeled motion generator and legged motion generator, and improve control efficiency.

Elastodynamics of a parallel Schönflies-motion generator

The authors propose a model of the elastodynamics of the Peppermill Carrier, a parallel isostatic Schönflies-motion generator designed for pick-and-place operations. The Cartesian spring and the finite element method are used to build the elastodynamics model of the robot. The stiffness and mass matrices are introduced to obtain the natural frequencies of the robot along a test trajectory — the Adept test cycle — that serves to evaluate the performance of the robot with respect to the operation speed.